It is known to track and attempt to locate objects, such as sales goods, components, medical samples, documents, produce or other articles of commerce, during their manufacture, storage, transport and/or distribution. Wireless communication transponders may be attached to or associated with such objects to provide information about the objects such as their identification number, expiration date, date of manufacture, lot number, and the like. An example of such a wireless communication transponder is a radio frequency identification (RFID) tag.
In order to communicate with the wireless communication transponders, a wireless transmission interrogator is placed in proximity to the objects. An example of such a wireless transmission interrogator is an RFID reader. The RFID reader creates a radio frequency field with appropriate radio circuitry and an antenna to communicate with the RFID tag and to identify the object the tag is associated with.
There are generally three different types of RFID tags: active RFID tags; passive RFID tags; and battery assisted passive (BAP) RFID tags. Active RFID tags contain a battery and can transmit signals autonomously. Passive RFID tags have no battery and require an external source, typically a signal transmitted by the interrogator, to power signal transmission. BAP RFID tags require an external source to activate the tag, but their battery powers their transmission resulting in it having a greater range of operation.
However, all three types of RFID tags are designed to operate at relatively short range. Accordingly, the RFID reader's antenna must be placed into relatively close proximity to the RFID tag in order to read it. In order to address this, different antennas have been developed to provide different radio frequency field sizes for reading the RFID tags in different use cases.
Unfortunately, antennas that have a large field size typically have a low resolution. That is, for example, an antenna with a large field size could be used to locate a target box from within a plurality of boxes, but it probably could not locate a target item from within the target box. Conversely, an antenna with a relatively small field size could locate a target item from within a box of items, but could not locate the box containing the target item from a collection of possible target boxes. Thus, different antennas, or different RFID readers altogether, may need to be used to locate both the target box and the target item or for other particular use cases.